Hereinafter, a carrier will be briefly described.
A user may perform a modulation operation with respect to the amplitude, frequency and/or phase of a sine wave and a periodic pulse wave. A sine wave or a pulse wave for carrying information is called a carrier.
Examples of a carrier modulation scheme include a Single-Carrier Modulation (SCM) scheme and a Multi-Carrier Modulation (MCM) scheme. Among others, the SCM scheme involves performing modulation with respect to all information carried on one carrier.
The MCM scheme refers to a technology of dividing an overall bandwidth channel of one carrier into several sub-channels each having a small bandwidth and transmitting a plurality of narrowband sub-carriers through the sub-channels.
In the MCM scheme, each of the sub-channels is approximated to a flat channel due to the limited bandwidth.
A user can compensate for channel distortion using a simple equalizer. In addition, the MCM scheme is implemented at a high speed using Fast Fourier Transform (FFT) and is more advantageous in high-speed data transmission than the SCM scheme.
As capabilities of a base station and/or a terminal have been developed, an available frequency bandwidth of the base station and/or the terminal has been expanded. Accordingly, in the embodiments of the present invention, a multi-carrier system supporting a wideband by aggregating one or more carriers is disclosed.
That is, in the following multi-carrier system, one or more carriers are aggregated and used, unlike the MCM scheme of dividing one carrier into sub-carriers and utilizing the sub-carriers.
In order to efficiently utilize multiple bands or multiple carriers, a technique of managing several carriers (e.g., several frequency carriers (FC)) by one medium access control (MAC) entity has been proposed.
FIGS. 1(a) and 1(b) are diagrams illustrating a method of transmitting or receiving a signal based on a multi-band radio frequency (RF).
In FIG. 1, in a transmitter and a receiver, one MAC layer may manage several carriers in order to efficiently use multiple carriers. In order to efficiently transmit or receiver multiple carriers, it is assumed that both the transmitter and the receiver can transmit or receive multiple carriers. Since the FCs managed by one MAC layer do not need to be contiguous with each other, flexible resource management is possible. That is, both contiguous aggregation and non-contiguous aggregation are possible.
In FIGS. 1(a) and 1(b), a physical layer (PHY) 0, a physical layer 1, . . . , a physical layer n-2 and a physical layer n-1 represent multiple bands of the present technique and each band may have an FC size assigned for a specific service according to a predetermined frequency policy. For example, the physical layer 0 (RF carrier 0) may have a frequency band size assigned for a general FM radio broadcast and the physical layer 1 (RF carrier 1) may have a frequency band size assigned for mobile telephone communication.
The frequency bands may have different frequency band sizes according to frequency band characteristics. However, in the following description, for convenience of description, it is assumed that each FC has a size of A [MHz]. Each frequency assignment band may be a carrier frequency for utilizing a baseband signal in each frequency band. Hereinafter, each frequency assignment band is referred to as “carrier frequency band” or simply “carrier” representative of each carrier frequency band if such use will not lead to confusion. Recently, as in the 3GPP LTE-A, the above carrier may be referred to as a “component carrier” in order to be distinguished from a subcarrier used in an MCM scheme.
Therefore, the above “multi-band” scheme may be referred to as a “multi-carrier” scheme or a “carrier aggregation” scheme.
In order to transmit a signal through multiple bands as shown in FIG. 1(a) and receive a signal through multiple bands as shown in FIG. 1(b), the transmitter/receiver needs to include an RF module for transmitting the signal through the multiple bands. In FIG. 1, the method of configuring “MAC” is determined by a base station regardless of downlink (DL) and uplink (UL).
In brief, the present technique refers to a technique for enabling one MAC entity to manage a plurality of RF carriers so as to transmit/receive a signal. The RF carriers managed by one MAC do not need to be contiguous with each other. According to the present technique, more flexible resource management is possible.
FIG. 2 is a diagram showing an example of a method of assigning a frequency in a multi-carrier system.
In FIG. 2, frequency carriers 0 to 7 may be managed by RFs 0 to 7. In the example of FIG. 2, it is assumed that the frequency carrier 0, the frequency carrier 2, the frequency carrier 3, the frequency carrier 6 and the frequency carrier 7 are already assigned to specific communication services. Available frequency carriers 1, 4 and 5 may be efficiently managed by one MAC (MAC #5). Since the frequency carriers configuring one MAC may not contiguous with each other as described above, it is possible to more efficiently manage frequency resources.
The above-described multi-band communication scheme is only conceptually defined and, as necessary, only frequency carriers may be further assigned. Therefore, it is necessary to define a signal transmission/reception scheme capable of achieving more efficient, high-capability processing.
In the above-described multi-band communication scheme, it is necessary to define a method of selecting carriers from among a plurality of available carriers of a base station in order to perform initial access.